This project is concerned with studies of various aspects of hypothalamic-pituitary-thyroid physiology in health and disease. Specific areas of current and planned investigation include: 1) Determination of the metabolic and hormonal consequences of the reduction of extrathyroidal production of triiodothyronine (T3) from thyroxine (T4) that occurs during starvation and illness in animals and man. 2) Studies of T3 production from T4 and the physiological regulation of this reaction in rat liver and kidney perfusion systems. 3) Purification of the rat liver and kidney T4-5'-deiodinating enzyme(s). 4) Prospective studies of the utility of measurements of serum thyroglobulin as an indicator of remission of hyperthyroidism due to Graves' disease during antithyroid drug therapy and comparison of the antithyroid effects of methimazole and propylthiouracil. 5) Further attempts to develop simple methods for the measurement of thyrotropin-releasing hormone (TRH) in biological fluids and purification of serum TRH degrading enzyme(s).